This invention relates to a non-destructive method of testing an evacuated package for a leak. More particularly it relates to a method for detecting in a non-destructive manner the presence of a leak in a package comprising an evacuated bag containing a charge of a comminuted product.
It is known to package a comminuted product, such as roast and ground coffee, in a sealed evacuated bag. For aesthetic reasons and for convenience of packing such packages in cartons, it is conventional practice to impart to the evacuated package a regular shape, for example a rectangular parallelepipedal shape. Such packages typically contain, for example, 250 g or 500 g of roast and ground coffee. A properly evacuated and sealed package is hard to the touch and resembles a brick. It is, however, difficult to ensure that every package produced is free from leaks. This is because the particles of roast and ground coffee are relatively light and the surface of a charge of coffee in a bag being sealed can be disturbed in the course of evacuating the bag, with the resultant danger of coffee particles being deposited upon the inside surface of the bag where the seal is to be formed. If there are coffee particles in this area, then the seal may not be properly formed and a leak may ensue. A coffee package with a leaking bag will feel softer to the touch than one with a properly evacuated leak-free bag and will have a shorter shelf life. In addition any aroma components introduced into the bag during the packaging operation can escape from a package with a leak with the result that the product may be less appealing to a consumer. In addition a package with a leak in it, i.e. with a loss of a barrier to oxygen, will result in rancidity in the coffee due to the deleterious effects of oxygen upon the coffee.
A number of proposals have been made for detecting the presence of a leak in coffee packages comprising evacuated bags. These generally rely upon contacting the evacuated and sealed bags with a lightly sprung mechanical probe or with an air jet. An example of such an arrangement is described in U.S. Pat. No. 4,517,827.
It is an object of the invention to provide a method for the non-destructive leak testing of evacuated sealed packages comprising a sealed evacuated bag containing a charge of a comminuted product such as roast and ground coffee.
It is a further object of the invention to provide a simple non-destructive method of testing sealed evacuated bags of a comminuted product for the presence of a leak which obviates the need for complex mechanical devices for probing the packages.
It is a still further object of the present invention to provide a more sensitive method of detecting in a non-destructive manner the presence of a leak in an evacuated flexible package containing roast and ground coffee than conventional prior art methods.
According to the present invention there is provided a method of non-destructive testing an evacuated package for the presence of a leak, said evacuated package comprising a sealed filled evacuated bag containing a predetermined quantity of a comminuted product, which comprises:
causing a surface of a sealed filled evacuated bag under test to impact under controlled conditions with a supported piezo electric device, and
measuring a resultant transient electrical test signal.